The present invention relates to a driving wheel slip control device for a vehicle.
A so-called traction control system is known from Japanese Patent Laid-open Publication No. 60-143171, for example. In the traction control system, when excess slip is generated in a driving wheel, fuel supply is cut off to reduce an engine output and thereby eliminate the excess slip.
However, such fuel supply reduction (including a reduction of the fuel supply) with respect to the engine is carried out when the driving wheel is in a slip condition, that is, when the engine is in a high load condition. Under such a condition of the engine, a fuel component in a combustion chamber of the engine is reduced because of the fuel supply reduction, causing an increase in resistance (or insulation resistance) at an ignition plug gap. The insulation resistance is increased with an increase in pressure in the combustion chamber. Therefore, the higher the engine load, the more the insulation resistance. Further, the insulation resistance becomes high when the ignition timing is near top dead center in a compression stroke. Accordingly, if a spark is emitted at the plug gap under the condition where the insulation resistance is high, as mentioned above, a demanded voltage (dielectric breakdown voltage) at the plug gap is rendered as high as 30 KV or more. As a result, there is a possibility of dielectric breakdown being generated at other portions besides the plug gap, such as between a high-tension cord-plug connecting portion and an engine block or in an ignition coil.